1. Field of the Invention
The present invention generally relates to a flow control protocol for a data transmission network and, more particularly, to a flow control over Fiber optic Distributed Data Interface (FDDI) synchronous networks and is specifically advantageous in teleconferencing and other multi-media applications requiring synchronous as opposed to asynchronous data transmission.
2. Description of the Prior Art
Local Area Networks (LANs) have long provided a medium for sharing data supporting electronic mail (E-mail) among people, but with the advent of multimedia applications supporting audio and video data, real time teleconferencing is now possible. The integration of audio and video in networked personal computers (PCs) enables many new kinds of collaborative work. Built-in video capabilities can support analog video signals from cable or a video cassette recorder (VCR), for example, or digital video from compact disk read only memory (CD-ROM). This in turn makes possible desktop video and document conferencing systems that support collaborative document mark-up and real-time video-in-a-window. In a typical document conferencing application, a "master" user owns the document and runs the application that created it, and one or more "slave" users see a bit-mapped image of the document that they can mark up and annotate in real time. There may be multiple simultaneous masters and slaves, allowing one node of a network to share a spreadsheet with other nodes while another node shares a document which may either reference the spreadsheet or import data from the spreadsheet.
"Whiteboarding" is the ability to draw or type on a blank white window on the video screen in an "ink" color-coded by the user. International Business Machines Corp. (IBM) sells a whiteboarding and document-sharing package, Person-to-Person/2, for its OS/2 operating system that also supports live videoconferencing via IBM's Action-Media II card. This package allows a plurality of users to share a common chalkboard or to mark up documents at the same time. The number of users, however, is limited by the token ring and ethernet LANs on which it runs.
There are many similarities between the FDDI standard and the IEEE 802.5 token-ring standard, but there are some significant differences, chief among which is bandwidth. Communication volume over a LAN is limited by the transmission medium and also by the topology and the relevant protocols at both the physical and medium access control levels. "Bandwidth" is a measure of the communication capacity of a LAN and is commonly given in bits per second (bps). For example, the bandwidth of a coaxial cable ethernet LAN may be 10 million bits per second (Mbps) while a Fiber optic Distributed Data Interface (FDDI) LAN using a timed-token protocol may be 100 Mbps. In addition to bandwidth, FDDI LANs also typically support a greater number of stations with greater reliability, due in part to the "self healing" properties designed into the FDDI ring. The FDDI standard was established by the American National Standards Institute (ANSI) and approved for international use by the International Standards Organization ISO).
FDDI synchronous transmission provides a near constant, low latency service for those applications requiring synchronous data transmission under various loads and configurations. An end station in an FDDI synchronous network must not exceed its synchronous bandwidth allocation on any given transmission opportunity. However, the end station must account for a variable bit rate from a particular multi-media session and also for the simultaneous variation of the throughput as other multi-media sessions are opened and closed. Another factor related to the transmission of data onto the media is the asynchronous nature of the arrival of the transmission opportunity.